Components in gas turbines, especially in aircraft engines, are subject to wear and tear during operation due to erosive substances, for example, sand or dust or ice. In the front part of the gas turbine, the area of the compressor, erosion generally causes a flattening of the flow leading edges of the compressor blades. When the compressor blades are not yet worn down, they have an aerodynamically optimized profile that is detrimentally affected by the wear. As a consequence of such the deterioration of the aerodynamic profile, the gas turbine loses efficiency, which means that the gas turbine needs more fuel to generate the same power. Therefore, from a financial point of view, it is desirable to counteract the wear of compressor blades, especially a deterioration of the aerodynamically optimized blade geometries. For this purpose, repair methods have become common practice that are aimed at once again providing damaged compressor blades with the most aerodynamically optimized geometries possible. A common repair method for compressor blades is, for example, grinding the leading edge of compressor blades. This grinding procedure rounds and smoothes the flattened profile areas and the roughened surfaces of these areas. A device for such a repair method for turbine blades that is based on the grinding of the flow leading edges is described, for example, in U.S. Pat. No. 6,302,625 B1. Generally speaking, turbine blades can refer to any blades that are used in a gas turbine. For the person skilled in the art, however, turbine blades are generally only those that are used in the area of the turbine of the engine, whereas compressor blades are only used in the area of the compressor. However, the term gas turbine blades will be used below to refer to compressor blades (including fan blades) as well as to turbine blades.
One problem encountered with such repair methods lies in the nature of the grinding process. Grinding is a metal-cutting process, that is to say, material is ground off until an aerodynamically advantageous leading edge is obtained. The loss of the basic material of the gas turbine blade during the grinding procedure, however, can be about equal to the loss of basic material due to the erosion itself. Consequently, erosive wear during operation removes basic material from the gas turbine blade, and then subsequently, a comparable quantity of basic material is once again removed during the standard repair procedure. Thus, this two-fold reduction of material has the direct effect of shortening the chord length of the gas turbine blade, in other words, as seen in the flow direction, the gas turbine blade becomes shorter or the effective surface of the gas turbine blade is diminished, which, in turn, as a rule, causes a further reduction in the efficiency and/or aerodynamic stability (regarding the stall margin, i.e. the safety margin to the turbine blade stall) of the gas turbine blades. This effect occurs every time a repair is carried out until the chord length is so short that, for example, a compressor blade can no longer be used. In this context, nicks or dents caused, for example, when rocks and birds are sucked into the gas turbine blades, result in an especially pronounced shortening of the chord length. Since such nicks generally have a very negative impact on the mechanical and aerodynamic properties of the gas turbine blades, a great deal of material has to be removed from the gas turbine blades until the nick is completely ground away or rounded off over a large surface area. Moreover, the pure loss of mass, that is to say, the reduction in weight of the gas turbine blade is problematic, irrespective of the above-mentioned change in the component geometry. If, for example, compressor blades are ground down on an assembled engine, that is to say, on an aircraft engine that is still attached to the wing of the aircraft (‘on wing’), then unbalances can arise since different amounts of material are removed from the individual compressor blades. In repair methods in which the gas turbine blades are dismantled from the gas turbine, unbalances can be reduced by a process of weighing and subsequent weight-specific distribution. However, such repair methods that involve dismantling the gas turbine are also many times more laborious and can only be carried out on site with great difficulty or not at all.